/*
Copyright 2014 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package scheduler

import (
	"time"

	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/util/runtime"
	"k8s.io/apimachinery/pkg/util/sets"
	"k8s.io/apimachinery/pkg/util/wait"
	"k8s.io/client-go/tools/cache"
	"k8s.io/client-go/tools/record"
	"k8s.io/kubernetes/pkg/api"
	"k8s.io/kubernetes/pkg/api/v1"
	"k8s.io/kubernetes/pkg/client/clientset_generated/clientset"
	corelisters "k8s.io/kubernetes/pkg/client/listers/core/v1"
	"k8s.io/kubernetes/plugin/pkg/scheduler/algorithm"
	schedulerapi "k8s.io/kubernetes/plugin/pkg/scheduler/api"
	"k8s.io/kubernetes/plugin/pkg/scheduler/core"
	"k8s.io/kubernetes/plugin/pkg/scheduler/metrics"
	"k8s.io/kubernetes/plugin/pkg/scheduler/schedulercache"
	"k8s.io/kubernetes/plugin/pkg/scheduler/util"

	"github.com/golang/glog"
)

// Binder knows how to write a binding.
type Binder interface {
	Bind(binding *v1.Binding) error
}

// PodConditionUpdater updates the condition of a pod based on the passed
// PodCondition
type PodConditionUpdater interface {
	Update(pod *v1.Pod, podCondition *v1.PodCondition) error
}

// Scheduler watches for new unscheduled pods. It attempts to find
// nodes that they fit on and writes bindings back to the api server.
type Scheduler struct {
	config *Config
}

// StopEverything closes the scheduler config's StopEverything channel, to shut
// down the Scheduler.
func (sched *Scheduler) StopEverything() {
	close(sched.config.StopEverything)
}

// Configurator defines I/O, caching, and other functionality needed to
// construct a new scheduler. An implementation of this can be seen in
// factory.go.
type Configurator interface {
	GetPriorityFunctionConfigs(priorityKeys sets.String) ([]algorithm.PriorityConfig, error)
	GetPriorityMetadataProducer() (algorithm.MetadataProducer, error)
	GetPredicateMetadataProducer() (algorithm.MetadataProducer, error)
	GetPredicates(predicateKeys sets.String) (map[string]algorithm.FitPredicate, error)
	GetHardPodAffinitySymmetricWeight() int
	GetSchedulerName() string
	MakeDefaultErrorFunc(backoff *util.PodBackoff, podQueue *cache.FIFO) func(pod *v1.Pod, err error)

	// Probably doesn't need to be public.  But exposed for now in case.
	ResponsibleForPod(pod *v1.Pod) bool

	// Needs to be exposed for things like integration tests where we want to make fake nodes.
	GetNodeLister() corelisters.NodeLister
	GetClient() clientset.Interface
	GetScheduledPodLister() corelisters.PodLister

	Create() (*Config, error)
	CreateFromProvider(providerName string) (*Config, error)
	CreateFromConfig(policy schedulerapi.Policy) (*Config, error)
	CreateFromKeys(predicateKeys, priorityKeys sets.String, extenders []algorithm.SchedulerExtender) (*Config, error)
}

// Config is an implementation of the Scheduler's configured input data.
// TODO over time we should make this struct a hidden implementation detail of the scheduler.
type Config struct {
	// It is expected that changes made via SchedulerCache will be observed
	// by NodeLister and Algorithm.
	SchedulerCache schedulercache.Cache
	// Ecache is used for optimistically invalid affected cache items after
	// successfully binding a pod
	Ecache     *core.EquivalenceCache
	NodeLister algorithm.NodeLister
	Algorithm  algorithm.ScheduleAlgorithm
	Binder     Binder
	// PodConditionUpdater is used only in case of scheduling errors. If we succeed
	// with scheduling, PodScheduled condition will be updated in apiserver in /bind
	// handler so that binding and setting PodCondition it is atomic.
	PodConditionUpdater PodConditionUpdater

	// NextPod should be a function that blocks until the next pod
	// is available. We don't use a channel for this, because scheduling
	// a pod may take some amount of time and we don't want pods to get
	// stale while they sit in a channel.
	NextPod func() *v1.Pod

	// WaitForCacheSync waits for scheduler cache to populate.
	// It returns true if it was successful, false if the controller should shutdown.
	WaitForCacheSync func() bool

	// Error is called if there is an error. It is passed the pod in
	// question, and the error
	Error func(*v1.Pod, error)

	// Recorder is the EventRecorder to use
	Recorder record.EventRecorder

	// Close this to shut down the scheduler.
	StopEverything chan struct{}
}

// NewFromConfigurator returns a new scheduler that is created entirely by the Configurator.  Assumes Create() is implemented.
// Supports intermediate Config mutation for now if you provide modifier functions which will run after Config is created.
func NewFromConfigurator(c Configurator, modifiers ...func(c *Config)) (*Scheduler, error) {
	cfg, err := c.Create()
	if err != nil {
		return nil, err
	}
	// Mutate it if any functions were provided, changes might be required for certain types of tests (i.e. change the recorder).
	for _, modifier := range modifiers {
		modifier(cfg)
	}
	// From this point on the config is immutable to the outside.
	s := &Scheduler{
		config: cfg,
	}
	metrics.Register()
	return s, nil
}

// Run begins watching and scheduling. It waits for cache to be synced, then starts a goroutine and returns immediately.
func (sched *Scheduler) Run() {
	if !sched.config.WaitForCacheSync() {
		return
	}

	go wait.Until(sched.scheduleOne, 0, sched.config.StopEverything)
}

// Config return scheduler's config pointer. It is exposed for testing purposes.
func (sched *Scheduler) Config() *Config {
	return sched.config
}

// schedule implements the scheduling algorithm and returns the suggested host.
func (sched *Scheduler) schedule(pod *v1.Pod) (string, error) {
	host, err := sched.config.Algorithm.Schedule(pod, sched.config.NodeLister)
	if err != nil {
		glog.V(1).Infof("Failed to schedule pod: %v/%v", pod.Namespace, pod.Name)
		copied, cerr := api.Scheme.Copy(pod)
		if cerr != nil {
			runtime.HandleError(err)
			return "", err
		}
		pod = copied.(*v1.Pod)
		sched.config.Error(pod, err)
		sched.config.Recorder.Eventf(pod, v1.EventTypeWarning, "FailedScheduling", "%v", err)
		sched.config.PodConditionUpdater.Update(pod, &v1.PodCondition{
			Type:    v1.PodScheduled,
			Status:  v1.ConditionFalse,
			Reason:  v1.PodReasonUnschedulable,
			Message: err.Error(),
		})
		return "", err
	}
	return host, err
}

// assume signals to the cache that a pod is already in the cache, so that binding can be asnychronous.
// assume modifies `assumed`.
func (sched *Scheduler) assume(assumed *v1.Pod, host string) error {
	// Optimistically assume that the binding will succeed and send it to apiserver
	// in the background.
	// If the binding fails, scheduler will release resources allocated to assumed pod
	// immediately.
	assumed.Spec.NodeName = host
	if err := sched.config.SchedulerCache.AssumePod(assumed); err != nil {
		glog.Errorf("scheduler cache AssumePod failed: %v", err)

		// This is most probably result of a BUG in retrying logic.
		// We report an error here so that pod scheduling can be retried.
		// This relies on the fact that Error will check if the pod has been bound
		// to a node and if so will not add it back to the unscheduled pods queue
		// (otherwise this would cause an infinite loop).
		sched.config.Error(assumed, err)
		sched.config.Recorder.Eventf(assumed, v1.EventTypeWarning, "FailedScheduling", "AssumePod failed: %v", err)
		sched.config.PodConditionUpdater.Update(assumed, &v1.PodCondition{
			Type:    v1.PodScheduled,
			Status:  v1.ConditionFalse,
			Reason:  "SchedulerError",
			Message: err.Error(),
		})
		return err
	}

	// Optimistically assume that the binding will succeed, so we need to invalidate affected
	// predicates in equivalence cache.
	// If the binding fails, these invalidated item will not break anything.
	if sched.config.Ecache != nil {
		sched.config.Ecache.InvalidateCachedPredicateItemForPodAdd(assumed, host)
	}
	return nil
}

// bind binds a pod to a given node defined in a binding object.  We expect this to run asynchronously, so we
// handle binding metrics internally.
func (sched *Scheduler) bind(assumed *v1.Pod, b *v1.Binding) error {
	bindingStart := time.Now()
	// If binding succeeded then PodScheduled condition will be updated in apiserver so that
	// it's atomic with setting host.
	err := sched.config.Binder.Bind(b)
	if err := sched.config.SchedulerCache.FinishBinding(assumed); err != nil {
		glog.Errorf("scheduler cache FinishBinding failed: %v", err)
	}
	if err != nil {
		glog.V(1).Infof("Failed to bind pod: %v/%v", assumed.Namespace, assumed.Name)
		if err := sched.config.SchedulerCache.ForgetPod(assumed); err != nil {
			glog.Errorf("scheduler cache ForgetPod failed: %v", err)
		}
		sched.config.Error(assumed, err)
		sched.config.Recorder.Eventf(assumed, v1.EventTypeWarning, "FailedScheduling", "Binding rejected: %v", err)
		sched.config.PodConditionUpdater.Update(assumed, &v1.PodCondition{
			Type:   v1.PodScheduled,
			Status: v1.ConditionFalse,
			Reason: "BindingRejected",
		})
		return err
	}

	metrics.BindingLatency.Observe(metrics.SinceInMicroseconds(bindingStart))
	sched.config.Recorder.Eventf(assumed, v1.EventTypeNormal, "Scheduled", "Successfully assigned %v to %v", assumed.Name, b.Target.Name)
	return nil
}

// scheduleOne does the entire scheduling workflow for a single pod.  It is serialized on the scheduling algorithm's host fitting.
func (sched *Scheduler) scheduleOne() {
	pod := sched.config.NextPod()
	if pod.DeletionTimestamp != nil {
		sched.config.Recorder.Eventf(pod, v1.EventTypeWarning, "FailedScheduling", "skip schedule deleting pod: %v/%v", pod.Namespace, pod.Name)
		glog.V(3).Infof("Skip schedule deleting pod: %v/%v", pod.Namespace, pod.Name)
		return
	}

	glog.V(3).Infof("Attempting to schedule pod: %v/%v", pod.Namespace, pod.Name)

	// Synchronously attempt to find a fit for the pod.
	start := time.Now()
	suggestedHost, err := sched.schedule(pod)
	metrics.SchedulingAlgorithmLatency.Observe(metrics.SinceInMicroseconds(start))
	if err != nil {
		return
	}

	// Tell the cache to assume that a pod now is running on a given node, even though it hasn't been bound yet.
	// This allows us to keep scheduling without waiting on binding to occur.
	assumedPod := *pod
	// assume modifies `assumedPod` by setting NodeName=suggestedHost
	err = sched.assume(&assumedPod, suggestedHost)
	if err != nil {
		return
	}

	// bind the pod to its host asynchronously (we can do this b/c of the assumption step above).
	go func() {
		err := sched.bind(&assumedPod, &v1.Binding{
			ObjectMeta: metav1.ObjectMeta{Namespace: assumedPod.Namespace, Name: assumedPod.Name, UID: assumedPod.UID},
			Target: v1.ObjectReference{
				Kind: "Node",
				Name: suggestedHost,
			},
		})
		metrics.E2eSchedulingLatency.Observe(metrics.SinceInMicroseconds(start))
		if err != nil {
			glog.Errorf("Internal error binding pod: (%v)", err)
		}
	}()
}
